Beyond Arduino

What it is: The Uno isn't the only Arduino product out there. Arduino currently makes 15 boards and is working on two more.
What it does: Some boards, like the Micro or Nano, are essentially the same but a different size. Others, like the Yun, have increased functionality with built-in USB, Wifi, or Ethernet support.
Where to get it: Check out the Arduino products page to learn more about the boards. You can also check the Adafruit, Sparkfun, or Lifehacker Arduino selection guides.
Learn to use it: Most Arduino boards run using the same software, so you already know the basics. Look up your board for more specific information.
Project ideas: Read the Further Reading page on this site for Arduino project ideas - many are written for different platforms than the Uno.

What it is: Probably the most popular microcontroller apart from the Arduino. It's significantly more powerful and basically has all the functionality of a real computer.
What it does: You can use your Raspberry Pi to surf the web, play games, watch videos, or use a word processor - basically anything you could do with a real computer. However, it's more complicated than the Arduino to use - it runs on Linux, so you'll need to be comfortabl with programming first.
Where to get it: First, read a guide like this or this to decide whether a Pi is right for you. You can buy one here.
Learn to use it: The Raspberry Pi website has a guide on setting up your Pi here. You can also check Adafruit or something similar for more tutorials.
Project ideas: Adafruit, Instructables, Lifehacker, Raspberry Pi HQ, and Make all have great collections of projects ideas, guides, and tutorials.

What it is: A flexible Arduino board designed for wearable applications. You can sew it into clothing or other textiles for electronic cloth.
What it does: LilyPads allow you to create light-up biking jackets, internet-connected t-shirts, or location-finding backpacks. If you can think of a clothing-based application, LilyPad helps you create it.
Where to get it: LilyPads are Arduino products and can be bought from the Arduino website. The Adafruit Flora is another similar wearable device.
Learn to use it: The LilyPad website takes you through the basics of programming the LilyPad, as well as how to sew it into your clothing.
Project ideas: Check the LilyPad website, Sew Electric, Sparkfun, or Instructables for ideas.

What it is: TI's microcontroller of choice. Similar to Arduino and Raspberry Pi, but with different applications.
What it does: You can think of a Beagleboard as a combination of a Pi and an Arduino - it has the power of a Pi but the connection power of an Arduino. It's designed for experienced users rather than learners, so it's not for beginners. It's best for powerful applications without advanced graphics.
Where to get it: You can buy the Beaglebone from their website here.
Learn to use it: The BeagleBone website has an extensive tutorial on how to use their board. You can also check Adafruit or Make for other guides.
Project ideas: Projects can be found at BeagleBoard, Make, EETimes, Adafruit, or IntoRobotics.

What it is: A microcontroller similar to the Arduino but with built-in Internet connectivity.
What it does: Because it connects to the Internet, you can use Nanode to interface with web-based services so you can control your devices from the Web. It's a relatively new platform, so people are still coming up with new projects and applications for the Internet of Things.
Where to get it: The Nanode website has kits so you can build your own Nanode.
Learn to use it: The Nanode uses Arduino software, so you can already program it. To construct your Nanode from your kit, use the guides on the Nanode website.
Project ideas: Because Beaglebone is new, there aren't that many projects out there yet. The Nanode site is developing a projects section, and you can find more ideas here, here, or here.

What it is: This Arduino board on wheels simplifies robot set-up.
What it does: The Arduino Robot has all the functionality of an Arduino, but you don't have to connect it separately to a motor and wheels. It has a motor board, a control board, and multiple sensors built in.
Where to get it: Buy a robot board from the Arduino website.
Learn to use it: The Arduino Robot guide has information on how to set up and use your new board. Library documentation can be found here.
Project ideas: The Arduino Robot board has so many pre-installed sensors that it's basically already a project idea. Try googling for robot ideas on older platforms and see if you can adapt them to work with this board. In general, this should simplify a lot of applications.

What it is: Intel's microprocessor is certified to work with Arduino software.
What it does: Galileo is Linux-based but fully compatible with Arduino software. This makes it the first major collaboration between an established tech firm and an upstart firm like Arduino.
Where to get it: The Galileo page on the Intel site has links to all resailers at the bottom of the page.
Learn to use it: Intel has multiple resources for makers, including a setup guide and video tutorials. The software is exactly the same as Arduino's.
Project ideas: You can find project ideas on Intel's site as well as Hackster, Make, and Sparkfun. For a comparison of Galileo and Raspberry Pi, check this guide from Mouser.

Beyond ArduinoLearn about other microcontrollers you can use to continue with electrical engineering.